The present invention relates to a series regulator that is used for obtaining a stabilized power source in a compact device like a portable telephone.
Series regulators are provided in the form of ICs using bipolar transistors and unipolar transistors. Series regulators using bipolar transistors will be explained below as an example.
FIG. 5 is a circuit diagram showing a basic structure of a conventional series regulator. As shown in FIG. 5, a power transistor 503 is connected in series between an input terminal 501 to which a non-stabilized voltage Vin output from an external starting voltage source is applied and an output terminal 502 to which a stabilized voltage Vout is output. Input ends (emitters) of transistors E1, E2 and E3 that constitute a bias current circuit are connected to a line that connects the input terminal 501 and an input end (emitter) of the power transistor 503.
The transistor E1 and the transistors E2 and E3 that are in diode connection have their control ends (bases) connected in common to constitute a current mirror circuit. A constant-current source 504 is provided between an output end (collector) of the transistor E1 and the ground. An output end (collector) of the transistor E2 is connected to a reference voltage circuit 505 and a negative-phase input end of an amplifier 506. An output end (collector) of the transistor E3 is connected to a bias input end of the amplifier 506.
A series circuit of resistors R1 and R2 is provided between a line that connects an output end (collector) of the power transistor 503 and an output terminal 502 and the ground. A control end of the reistors R1 and R2 is connected to a positive-phase input end of the amplifier 506. An output end of the amplifier 506 is connected to a control end (base) of the power transistor 503.
In the series regulator having the above structure, when the external starting voltage source has started operation, a constant bias current is supplied to the reference voltage circuit 505 based on a current mirror operation of the transistors E1 and E2, and a reference voltage is supplied to the amplifier 506 from the reference voltage circuit 505. At the same time, a bias current is supplied to the amplifier 506 from the transistor E3, and the amplifier 506 starts the operation of changing the internal resistance of the power transistor 503. The output voltage of the power transistor 503 is supplied to the amplifier 506 after being divided by the series circuit of the resistors R1 and R2.
As a result, the amplifier 506 changes the internal resistance of the power transistor 503 based on the result of a comparison between the magnitude of the reference output voltage and the magnitude of the divided voltage, and output a stable constant output voltage Vout from the output terminal 502. As explained above, according to the conventional series regulator, the reference voltage circuit 505 and the amplifier 506 operate based on the bias current supplied from the input side.
However, when the power source of the external starting voltage source is turned on, the output voltage, that is, the input voltage Vin of the series regulator, varies in many cases, as shown in FIG. 6, for example. In this case, according to the conventional series regulator, the reference voltage circuit and the amplifier operate by receiving a supply of a bias current that varies following the variation in the input voltage Vin. Therefore, there occurs a fluctuation in the reference voltage, and a ripple is generated in the output voltage Vout as shown in FIG. 6. This becomes one of factors that aggravates a ripple removal ratio.
It is an object of the present invention to provide a series regulator capable of reducing a ripple voltage that appears in the output voltage due to a variation in the input voltage during a normal operation after a stable voltage has been obtained following the turning-on of the power source, and capable of improving a ripple removal ratio of the series regulator.
The series regulator according to one aspect of the present invention comprises: a power transistor connected in series between an input terminal to which a non-stabilized voltage is applied and an output terminal; an amplifier for changing an internal resistance of the power transistor based on a result of a comparison between an output voltage of the power transistor and a reference voltage, and outputting a stabilized constant voltage to the output terminal; a first bias current circuit for generating a bias current to be supplied to a reference voltage circuit that generates the reference voltage, based on a non-stabilized voltage applied to the input terminal; a resistance voltage dividing circuit for generating a divided voltage of a predetermined value from an output voltage of the power transistor; an output voltage detecting circuit including a first transistor to a control end of which there is applied a conversion voltage of a bias current that the first bias current circuit supplies to the reference voltage circuit; and a second transistor to a control end of which there is applied the divided voltage, wherein the output voltage detecting circuit having a differential structure such that the second transistor is turned on and the first transistor is turned off when the divided voltage has reached a value of the conversion voltage; a second bias current circuit for generating a bias current to be supplied to the reference voltage circuit in response to the on-operation of the second transistor, based on an output voltage of the power transistor; and a bias switching circuit for stopping a bias-current supply operation of the first bias current circuit in response to a starting of the operation of the second bias current circuit.
Thus, when a non-stabilized voltage has been applied to an input terminal, a bias current is supplied to a reference voltage circuit from a first bias current circuit provided at the input side. Then, an amplifier starts the control of a power transistor. In an output voltage detecting circuit, a first transistor is applied with a conversion voltage of a bias current at its control end, and is turned on. When the output voltage of the power transistor rises, and a value of a divided voltage generated by a resistance voltage dividing circuit has reached a value of a conversion voltage of the bias current, a second transistor is turned on in the output voltage detecting circuit. Therefore, a second bias current circuit starts supplying a bias current to the reference voltage circuit. At the same time, a bias switching circuit operates to stop the bias-current supply operation of the first bias current circuit.
The series regulator according to another aspect of the present invention comprises: a power transistor connected in series between an input terminal to which a non-stabilized voltage is applied and an output terminal; an amplifier for changing an internal resistance of the power transistor based on a result of a comparison between an output voltage of the power transistor and a reference voltage, and outputting a stabilized constant voltage to the output terminal; a resistance voltage dividing circuit for generating a divided voltage of a predetermined value from an output voltage of the power transistor; a first bias current circuit for generating a bias current to be supplied to a reference voltage circuit that generates the reference voltage, based on a non-stabilized voltage applied to the input terminal, the first bias current circuit for supplying a bias current to the reference voltage circuit during a period while a first transistor to a control end of which a conversion voltage of the bias current is applied is in on-operation; and a second bias current circuit for generating a bias current to be supplied to the reference voltage circuit, based on an output voltage of the power transistor, the second bias current circuit for supplying a bias current to the reference voltage circuit during a period while a second transistor to a control end of which the divided voltage is applied is in on-operation, wherein the first bias current circuit and the second bias current circuit are differentially structured such that the second transistor is turned on when the divided voltage has reached a value of the conversion voltage, and the first transistor is turned off following this.
Thus, a first bias current circuit provided at an input side and a second bias current circuit provided at an output side are differentially structured. Therefore, when a non-stabilized voltage has been applied to an input end, a first transistor is turned on, and a bias current is supplied from the first bias current circuit to a reference voltage circuit. Then, an amplifier starts controlling a power transistor. The first transistor is applied with a conversion voltage of the bias current, and continues the on-operation. A second transistor of the second bias current circuit that is differentially structured is in an off-status. When the output voltage of the power transistor rises, and a value of a divided voltage generated by a resistance voltage dividing circuit has reached a value of a conversion voltage of the bias current, the second transistor is turned on. Therefore, the second bias current circuit starts supplying a bias current to the reference voltage circuit. On the other hand, in the first bias current circuit, the first transistor is turned off. Therefore, the first bias current circuit stops supplying the bias current to the reference voltage circuit. In other words, as the first bias current circuit provided at the input side and the second bias current circuit provided at the output side are differentially structured, these bias current circuits constitute a bias switching circuit as a total system.
The series regulator according to another aspect of the present invention comprises: a first power transistor connected in series between an input terminal to which a non-stabilized voltage is applied and a first output terminal; a first amplifier for changing an internal resistance of the first power transistor based on a result of a comparison between an output voltage of the first power transistor and a reference voltage, and outputting a stabilized constant voltage to the first output terminal; a second power transistor connected in series between the input terminal and a second output terminal; a second amplifier for changing an internal resistance of the second power transistor based on a result of a comparison between an output voltage of the second power transistor and the reference voltage, and outputting a stabilized constant voltage to the second output terminal; a first resistance voltage dividing circuit for generating a first divided voltage of a predetermined value from an output voltage of the first power transistor, and a second resistance voltage dividing circuit for generating a second divided voltage of a predetermined value different from the first divided voltage, from an output voltage of the second power transistor; a first bias current circuit for generating a bias current to be supplied to a reference voltage circuit that generates the reference voltage, based on a non-stabilized voltage applied to the input terminal, the first bias current circuit for supplying a bias current to the reference voltage circuit during a period while a first transistor to a control end of which a conversion voltage of the bias current is applied is in on-operation; a second bias current circuit for generating a bias current to be supplied to the reference voltage circuit, based on an output voltage of the first power transistor, the second bias current circuit for supplying a bias current to the reference voltage circuit during a period while a second transistor to a control end of which the first divided voltage is applied is in on-operation; and a third bias current circuit for generating a bias current to be supplied to the reference voltage circuit, based on an output voltage of the second power transistor, the third bias current circuit for supplying a bias current to the reference voltage circuit during a period while a third transistor to a control end of which the second divided voltage is applied is in on-operation, wherein the first bias current circuit, the second bias current circuit, and the third bias current circuit are differentially structured such that only a corresponding one of the second transistor and the third transistor is turned on when either the first divided voltage or the second divided voltage having a higher value has first reached a value of the conversion voltage, and the first transistor is turned off following this.
Thus, a first bias current circuit provided at an input side, a second bias current circuit provided at one output side, a third bias current circuit provided at the other output side are differentially structured. Therefore, when a non-stabilized voltage has been applied to an input end, a first transistor is turned on, and a bias current is supplied from the first bias current circuit to a reference voltage circuit. Then, a first amplifier starts controlling a first power transistor, and a second amplifier starts controlling a second power transistor. The first transistor is applied with a conversion voltage of the bias current, and continues the on-operation. A second transistor of the second bias current circuit and a third transistor of the third bias current circuit that are differentially structured are in an off-status. When the output voltages of the first and second power transistors rise, and when either a first divided voltage generated by a first resistance dividing circuit or a second divided voltage generated by a second resistance dividing circuit having a higher value has first reached a value of the conversion voltage, the corresponding one of the second transistor and the third transistor is turned on. The first transistor is turned off following this. As a result, a bias current is supplied to the reference voltage circuit from the corresponding one of the second bias current circuit and the third bias current circuit. At the same time, the first bias current circuit stops supplying the bias current. Stabilized voltages are output from the two output terminals respectively. In other words, as the first bias current circuit provided at the input side, the second bias current circuit provided at one output side, and the third bias current circuit provided at the other output side are differentially structured, these bias current circuits constitute a bias switching circuit as a total system.
Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings.